Citation from Knowledge-Base Article 38754
“ArcSDE is based on the Open GIS Consortium Simple Feature Specification (OpenGIS Implementation Specification for Geographic Information - Simple Feature Access - Part 2: SQL option), which does not support parametric curves (this is also true of the other DBMS vendor spatial type implementations that are all OGC-based). As such, parametric curves are stored as densified arcs within ArcSDE. File and personal geodatabases support the storage of parametric curves and use the ArcObjects-based geometry engine for populating the Shape_Length and Shape_Area fields. The difference in parametric curve support is what causes the slight discrepancies in the Shape_Length and Shape_Area fields when comparing data stored in file/personal geodatabases with ArcSDE geodatabases. The amount of discrepancy is entirely dependent on the number and characteristics of the parametric curves in the geometry.“
For users, how are responsible for the Data and the Quality of them, it is not as important, if ArcSDE is OGC conform or not. This users expect the correct and exact value of Shape_Length and Shape_Area. Therefore, if ArcSDE should be OGC conform, we suggest and expect additional fields for Area and Length with the correct and exact values.
By the way, Personal and Filebased Geodatabases show the correct values for Shape_Length and Shape_Area also for objects with parametric curves!